The present invention relates to a tomograph for reconstructing a sectional radiograph or a tomogram of an object, from images of the object formed of radiation beams which have transmitted the object in a plurality of different directions, to inspect the inside of the object non-destructively, utilizing radiation such as X-rays, .gamma.-rays and a neutron beam.
In the conventional tomography utilizing X-rays, .gamma.-rays, or a neutron beam, images of a to-be-inspected object are formed of X-ray beams, .gamma.-ray beams, or neutron beams which have passed through the to-be-inspected object in a plurality of different directions, and a tomogram of the object is obtained by performing an arithmetic operation with data on the transmission of the object to provide transmission images. Each of the transmission images according to the conventional tomography indicates the absorptivity of the object with respect to X-rays, .gamma.-rays, or a neutron beam. Accordingly, the tomogram indicates the absorptivity distribution in a cross section of the object.
When a radiation beam such as an X-ray beam, a .gamma.-ray beam, or a neutron beam transmits through an object, both the amplitude and the phase of the beam are changed. It has been known that a change in the phase is generally greater than a change in the amplitude for the transmission beam. Accordingly, when a tomogram is formed by using a change in the phase, this tomogram would be higher in the contrast than conventional tomogram which uses a change in the amplitude. The tomogram based upon a change in the phase indicates the refractive-index distribution in a cross section of the object. As a measuring technique in which a change in the phase is used, there exists phase-contrast microscopy. However, as far as the present inventors know, tomography for reconstructing a tomogram by measuring and using a change in the phase does not exist at present.